1. Field of the Invention
This invention relates to an electromechanical actuator.
2. Description of the Related Art
Conventionally, a hydraulically driven actuator is used frequently as an actuator for use with a driving system for aircrafts, general industrial machinery and so forth. On the other hand, in the field of the aircraft technology, an electromechanical actuator (EMA) which can achieve reduction in weight in comparison with a hydraulically driven actuator and eliminates oil maintenance is and has been researched and developed, and it is being attempted to place an electromechanical actuator into practical use.
As an example of an electromechanical actuator, an electromechanical actuator can be listed which is configured such that a rod, that is, a threaded shaft member, is screwed in a rotatable member in the form of a nut which is rotated by a motor and, based on a feed amount of the rod per one rotation of the motor, the rod is moved in an axial direction in response to the angle of rotation of the motor. In this manner, in the electromechanical actuator configured using the mechanism described above, that is, a ball screw mechanism, in this manner, one end portion of the rod functions as a driving portion.
Another electromechanical actuator is known which adopts a dual mechanism having two driving systems each including a motor and a ball screw from the point of view of failsafe such that a failure such as jamming occurs with one of the systems, the other system is rendered operative so that the operation function of the entire electromechanical actuator can be guaranteed. An electromechanical actuator of the type described is disclosed in Japanese Patent Application Laid-Open No. 2008-8470 (hereinafter referred to as Patent Document 1).
In particular, Patent Document 1 discloses an electromechanical actuator which includes a first system which in turn includes a first rotational member rotated by a first motor and a first outputting member which is moved back and forth in an axial direction by driving force outputted from the first motor through the first rotational member, and a second system having a configuration similar to that of the first system.
FIG. 5 shows an example of such an electromechanical actuator having two systems as described above. Referring to FIG. 5, the electromechanical actuator X′ shown is configured such that a first rod A2′ which serves as a first outputting member is moved back and forth in an axial direction by rotational driving force of a first motor A1′ of a first system A′, and a second rod B2′ which serves as a second outputting member is moved back and forth in an axial direction by rotational driving force of a second motor B1′ of a second system B′. The distance between a first driving section A3′ set to an end portion of the first rod A2′ and a second driving section B3′ set to an end portion of the second rod B2′ in FIG. 5 corresponds to a minimum stroke length St(d) of the electromechanical actuator X′. In the state in which the minimum stroke length St(d) is assured, the rods A2′ and B2′ are positioned nearest to each other. If the positions of the rods A2′ and B2′ in the state in which the minimum stroke length St(d) is assured are represented as minimum stroke positions (S), then the stroke length St of the electromechanical actuator X′ can be increased to a maximum stroke length St(d+α) illustrated in FIG. 6, for example, by driving the second motor B1′ from the state described to rotate in a predetermined direction to move the second rod B2′ from the first rod A2′ with respect to the minimum stroke position (S). It is to be noted that, in FIG. 6, the second driving section B3′ in a state in which the second rod B2′ is disposed at the minimum stroke position (S) is indicated by an alternate long and two short dashes line.
In this manner, the electromechanical actuator X′ is demanded that a minimum stroke length St(d) and a maximum stroke length St(d+α) be set in response to specifications and so forth and a stroke width can be adjusted suitably within a stroke range whose upper and lower limits are provided by the minimum stroke length St(d) and the maximum stroke length St(d+α).